[Federal Register Volume 79, Number 143 (Friday, July 25, 2014)]
[Rules and Regulations]
[Pages 43236-43237]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-17578]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2013-0911; Special Conditions No. 25-539-SC]
Special Conditions: Airbus Model A350-900 Airplanes; Lateral-Trim
Function Through Differential Flap Setting
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for Airbus Model A350-900
airplanes. These airplanes will have a novel or unusual design feature
associated with a lateral-trim function that deploys flaps
asymmetrically for airplane lateral-trim control. This function
replaces the traditional method of providing airplane lateral trim over
a small range through flap and aileron mechanical rigging. The
applicable airworthiness regulations do not contain adequate or
appropriate safety standards for this design feature. These special
conditions contain the additional safety standards that the
Administrator considers necessary to establish a level of safety
equivalent to that established by the existing airworthiness standards.
DATES: Effective Date: August 25, 2014.
FOR FURTHER INFORMATION CONTACT: Robert C. Jones, FAA, Propulsion and
Mechanical Systems, ANM-112, Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone (425) 227-1234; facsimile (425) 227-1320.
SUPPLEMENTARY INFORMATION:
Background
On August 25, 2008, Airbus applied for a type certificate for their
new Model A350-900 airplane. Later, Airbus requested, and the FAA
approved, an extension to the application for FAA type certification to
November 15, 2009. The Model A350-900 airplane has a conventional
layout with twin wing-mounted Rolls-Royce Trent XWB engines. It
features a twin-aisle, 9-abreast, economy-class layout, and
accommodates side-by-side placement of LD-3 containers in the cargo
compartment. The basic Model A350-900 airplane configuration
accommodates 315 passengers in a standard two-class arrangement. The
design cruise speed is Mach 0.85 with a maximum take-off weight of
602,000 lbs.
On conventional airplanes, small, lateral, airplane asymmetries
typically have been addressed through flap and aileron rigging (e.g.,
using shims). On Model A350-900 airplanes, an order for asymmetric flap
deployment will be computed by the primary flight-control system as a
function of the aileron position. The current airworthiness standards
do not contain adequate safety standards for asymmetric use of the
flaps for Airbus Model A350-900 airplanes. Special conditions are
needed to account for the aspects of a function used to command an
intended flap asymmetry. The lateral-trim function is intended to be
performed once during climb and once during cruise to compensate for
airplane small lateral asymmetries.
The lateral-trim function is not a trim-control system in the
conventional sense as it has no pilot interface and is not governed by
Title 14, Code of Federal Regulations (14 CFR) 25.677. Some fly-by-wire
airplanes have no pilot-operated lateral trim at all. The lateral-trim
function is simply an additional fly-by-wire flight-control function
that nulls small roll asymmetries in certain flight phases with small,
asymmetric flap deployments. Although the function operates under
normal conditions within the small range of the traditional rigging,
failure cases may result in a significant out-of-range asymmetric flap
condition. An asymmetry threshold protects the system against excessive
flap asymmetry.
Type Certification Basis
Under 14 CFR 21.17, Airbus must show that the Model A350-900
airplane meets the applicable provisions of 14 CFR part 25, as amended
by Amendments 25-1 through 25-129.
If the Administrator finds that the applicable airworthiness
regulations (i.e., 14 CFR part 25) do not contain adequate or
appropriate safety standards for the Model A350-900 airplane because of
a novel or unusual design feature, special conditions are prescribed
under Sec. 21.16.
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, the special conditions would also apply to the
other model under Sec. 21.101.
In addition to the applicable airworthiness regulations and special
conditions, the Model A350-900 airplane must comply with the fuel-vent
and exhaust-emission requirements of 14 CFR part 34, and the noise-
certification requirements of 14 CFR part 36. The FAA must issue a
finding of regulatory adequacy under Sec. 611 of Public Law 92-574,
the ``Noise Control Act of 1972.''
The FAA issues special conditions, as defined in 14 CFR 11.19,
under Sec. 11.38, and they become part of the type-certification basis
under Sec. 21.17(a)(2).
Novel or Unusual Design Features
The Airbus Model A350-900 airplane incorporates the following novel
or unusual design features: The asymmetric use of flaps to address
lateral trim, which is not adequately addressed by Sec. 25.701.
[[Page 43237]]
Discussion
Section 25.701(a) requires that, unless the airplane has safe-
flight characteristics with the flaps or slats retracted on one side
and extended on the other, flap and slat surfaces must be synchronized
by either a mechanical interconnection or any equivalent means that has
the same integrity. Synchronization is interpreted to mean that flap
movement is symmetrical throughout the full range of flap motion.
Because the lateral-trim function intentionally creates asymmetric flap
motions, the flap-system installation of the Model A350-900 airplane
does not meet the requirement of Sec. 25.701(a) and (d).
These special conditions contain the additional safety standards
that the Administrator considers necessary to establish a level of
safety equivalent to that established by the existing airworthiness
standards.
Discussion of Comments
Notice of proposed special conditions no. 25-13-22-SC for Airbus
Model A350-900 airplanes was published in the Federal Register on
January 8, 2014 (79 FR 1339). No comments were received, and the
special conditions are adopted as proposed.
Applicability
As discussed above, these special conditions apply to Airbus Model
A350-900 airplanes. Should Airbus apply later for a change to the type
certificate to include another model incorporating the same novel or
unusual design feature, the special conditions would apply to that
model as well.
Conclusion
This action affects only certain novel or unusual design features
on the Airbus Model A350-900 airplanes. It is not a rule of general
applicability.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type-certification basis for Airbus Model A350-900 airplanes:
Lateral-Trim Function Through Differential Flap Setting
Current airworthiness standards, specifically Sec. 25.701, do not
contain adequate safety standards for this airplane design. In lieu of
the requirements of Sec. 25.701(a) and (d) for the lateral-trim
function, the following special condition are issued:
1. Airbus must demonstrate that an unsafe condition is not created
by using the flaps asymmetrically.
2. The degree of acceptable asymmetry must be defined and justified
for all flight phases with respect to:
a. Section 25.701(b) and (c), with the worst-case asymmetric flap
configurations, and
b. Providing equivalent protection against excess asymmetry in the
same manner as Sec. 25.701 provides to systems that are synchronized,
or use another equivalent means to prevent asymmetry.
3. This lateral-trim function is a flight-control system and
therefore must be shown to comply with both general system requirements
as well as general flight-control requirements. Therefore, the function
must be demonstrated not to have significant latent failures, where
practicable.
Issued in Renton, Washington, on July 9, 2014.
Jeffrey E. Duven,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 2014-17578 Filed 7-24-14; 8:45 am]
BILLING CODE 4910-13-P